An Organic Light-Emitting Diode (i.e., OLED) is also referred to as an organic electroluminescent device, which has a basic structure thereof includes an anode, a cathode and a light-emitting layer that correspond to each pixel region. When a voltage is applied to the anode and the cathode, holes move to a light-emitting layer via a hole transport layer, and electrons move to the light-emitting layer via an electron transport layer, then the holes and the electrons are recombined in the light-emitting layer, and the excitons in the materials of the light-emitting layer transit from an excited state to a ground state so that light is emitted out.
When the light passes through the cathode, the electrons in the cathode that may move freely will interact with the photons, so as to generate an electron dilatational wave that propagates along the surface of the cathode metal, which is called a surface plasmon polariton. Thus, the light will lose a part of its energy when passing through the cathode metal layer. Therefore, at present, an optical coupling layer (CPL) is generally manufactured above the cathode, so that the generation of the surface plasmon polaritons will be suppressed, the loss of the light passing through the cathode metal layer will be reduced, thereby improving the light extraction efficiency. Also, the optical coupling layer with a high refractive index may also reduce the total reflection from the cathode and coupling layer interface on the light exit side, lower the optical waveguide effect in the device, thereby further improving the light extraction efficiency. However, for the light of different colors, the corresponding optimal thicknesses of the optical coupling layers are different, and the longer the wavelength is, the larger the corresponding optimal thickness of the optical coupling layer will be. Therefore, different thicknesses of the optical coupling layer needs to be provided for the pixel regions that emit light with different colors, and hence the manufacture cost of the organic light-emitting display panel will be increased.